This specification discloses novel means for treatment of acute vascular conditions which may arise from mechanical or chemical damage to the vascular system or that may arise from sudden decrease in blood supply to the brain, as occurs in obstructive stroke or damage to neuronal tissue that arises from neurotoxins by appropriate administration of neuregulin in accord with the teachings herein.
Neuregulins are a family of multipotent growth factors that includes acetylcholine receptor inducing activities (ARJAs), growth factors, heregulins, and neu differentiation factors. Neuregulins' effects appear to be mediated by interactionwith a class of tyrosine kinase receptors related to the epidermal growth factor receptor. Neuregulins stimulate the tyrosine phosphorylation of these receptors and the subsequent activation of various signal transduction mechanisms. Neuregulins are synthesized as transmembrane precursors consisting of either an immunoglobuline-like or cysteine-rich domain, and EGF-like domain a transmembrane domain and a cytoplastic tail. The EGF-like domain of NRG-1 appears to be sufficient for activation.
Neuregulin-1 (NRG-1) is expressed in vascular endothelial cells and its receptors are localized in the underlying smooth muscle cells. However, its use in treatment of acute conditions and for repair of damaged tissue by enhancing migration of stem cells to damaged areas to provide new neuronal tissue has not previously been disclosed.
Atherosclerosis is a major cause of death in Western civilizations, leading to both heart attack and strokes. Atherosclerosis is a complex, chronic inflammatory disease of the arterial vessel wall which involves multiple processes including endothelial dysfunction, inflammation, vascular smooth muscle cell (VSMC) proliferation, and matrix alteration. Damage to the endothelial lining of the arterial wall due to angioplasty, insertions of stents or catheters and atherosclerosis all induce the release of pro-inflammatory cytokines and growth factors that stimulate normally quiescent VSMC to migrate and proliferate. VSMC proliferate and migrate from the medial layer of the vessel into the intima resulting in neointimal hyperplasia, which is also a major cause of restenosis after angioplasty or cardiac surgery, especially surgery on the heart valves. Mitogens, such as platelet derived growth factor (PDGF), are potent stimulators of VSMC proliferation and differentiation following vascular injury. PDGF is produced by platelets, endothelial cells, smooth muscle cells and macrophages that infiltrate the artery in response injury and the release of PDGF afterlinjury contributes significantly to the formation of the neointima.
Ischemic stroke occurs when the blood supply to the brain is obstructed. The neuronal death that ensues results from the induction of genes associated with a number of additional cellular functions. A substantial body of research implicates inflammation as a contributor to stroke morbidity. Ischemic stroke initiates an inflammatory response in the injured brain and progresses for days after the onset of symptoms. There is evidence that inflammatory reactions are involved in the delayed ischemic injury and result in poor prognosis of neurological outcome.
In response to cerebral ischemia, inflammatory cytokines, such as tumor necrosis factor (TNFα) and interleukin-1β (IL-1β), are induced in the ischemic brain of animal models. Following ischemic injury, IL-1β and TNFα, have been shown to facilitate neuronal damage. These cytokines induce the expression of adhesion molecules, downstream pro-inflammatory molecules and stress genes.
Chemical cause of neuronal damage include neurotoxins such as those used in chemical warfare and in some pesticides. Recent studies have demonstrated the existence of neuronal injury secondary to the stimulation of cholinergic pathways, which is associated with pro-inflammatory processes in the CNS following exposure to Organophosphorus (OP). OP nerve agents are toxic chemicals that have been used by terrorists in military combat and against civilian populations. Current post-exposure medical counter-measures against nerve agents (e.g. atropine, oximes and benzodiazepines) are useful in preventing mortality, but are not sufficiently effective in protecting the CNS from seizures and permanent injury. Therefore, new and more effective medical countermeasures to avoid post-exposure damage to neuronal tissues are needed. Recent studies have demonstrated the existence of neuronal injury, secondary to the stimulation of cholinergic pathways, which is associated with pro-inflammatory processes in the CNS following exposure to OP nerve agents.
The neuregulins have been known to be involved in the survival and function of neuronal cells. A recent study using NRG-1 demonstrated the neuregulin blocked delayed neuronal death following focal ischemic stroke. However, the mechanisms that underlie the neuroprotective effects of NRG-1 are unclear. Neurogenesis has been described in the adult mammalian CNS in the subventricular zone (SVZ) and dentate gyrus of the hippocampus. Studies have shown that neurogenesis may be stimulated from multiple cell types in the SVZ. Four cell types are found in the SVZ: neuroblasts (type A), SVZ astrocytes (type B), rapidly dividing precursors (type C), and multiciliated ependymal cells. Each type is capable of giving rise to neurons and glia.
Stem cells research has attracted widespread attention and controversy over the past several years. Stem cells are undifferentiated, primitive cells with the ability to differentiate into various kinds of cells. Stem cells can be used to restore or regenerate tissue, which could be useful in treating injuries or disease. Stem cell research is controversial because the best source of true pluripotent stem cells is human fetal tissue, which is harvested from destroyed embryos. Unlike embryonic stem cells, adult stem cells are unspecialized, undifferentiated cells that exist in very small numbers among specialized cells in an adult organ or tissue. Their main function is to maintain and periodically repair the tissues in which they are found. Adult stem cells are found in a number of locations, including the brain, the bone marrow, peripheral blood, blood vessels, skeletal muscle, skin, and liver. There is no controversy regarding the use of human adult stem cells in research, since they can be retrieved from the individual requiring the therapy.
Neurogenesis in the adult brain normally also occurs in two regions of the adult mammalian brain; the olfactory bulb and the dentate gyrus of the hippocampus. The neural stem cells (NSCs) destined for the olfactory bulb originate from the subventricular zone (SVZ), which lies along the length of the lateral ventricle. In the developing CNS, NSCs comprise a self-renewing cell population able to generate neurons, astrocytes and oligodendrocytes. The newly generated olfactory bulb NSCs proliferate and migrate in the SVZ along the rostral migratory stream (RMS) towards the olfactory bulb. These NSCs differentiate into two kinds of inhibitory interneurons in the olfactory bulb. Four ceil types are found in the SVZ: neuroblasts (type A), SVZ astrocytes (type B), rapidly dividing precursors (type C), and multiciliated ependymal cells (EC) that line the ventricles. Focal clusters of rapidly dividing type C cells are found scattered along the RMS. The stem cells in the adult SVZ have been shown to be SVZ astrocytes in one study. SVZ astrocytes divide to give rise to rapidly dividing immature precursors (type C) that in turn generate the neurons that migrate to the olfactory bulb and differentiate into neuroblasts (type A). However, other reports suggest that EC may also serve as adult SVZ stem cells. New neurons in the hippocampus are derived from NSCs in the subgranular zone (SGZ) and give rise to granule cells that project to the CA3 region of the hippocampus. It has also been demonstrated that neurogenesis can occur in regions of the adult mammalian brain, like the neocortex, where it does not normally occur, via manipulation of endogenous multipotent precursors in situ.
NSCs of CNS are patterned in vivo to generate neurons, oligodendrocytes, and astrocytes. In vitro, pluripotent NSCs generate lineage-restricted, self-renewing neuron-restricted progenitors (NRPs), and glial-restricted progenitors (GRPs), which subsequently develop into fully differentiated neuron and glial cells, respectively. NRPs are mitotically active and electrically immature, and they express only a subset of neuronal markers. NRPs undergo additional changes to develop into mature, functional neurons, NSCs, NRPs, and GRPs have been previously isolated from mouse neural tubes that undergo self-renewal in defined medium, and differentiate into multiple neural phenotypes in mass culture. When isolated neuroepithelial NSCs are maintained in culture in the absence of a substrate that supports adhesion, cells form neurospheres. Neurospheres contain a relatively homogeneous population of NSCs that undergo self-renewal in response to either bFGF or EGF. It was observed, however, that after mitogen withdrawal, the NSCs were unable to undergo neuronal differentiation directly. These cells emerged from the neurosphere as NRPB. These NRPs were required to go through one or more rounds of cell division before neurogenesis could proceed to generate of neurons.